On Wed, 8 Nov 2000, Christian Holm Christensen wrote: > As far as I understand, the current primary vertex code chooses a > primary vertex from one of the 4 vertex algorithms, based on some > "goodness" criteria. Yes, but this is not necesearily meant to last. The module was actually "released" a bit prematurely since this part is not really ready, but I did it to make resolution-investigations etc. a bit easier. I agree in principal with using more than one method to fix the primary vertex, but with a few reservations: 1) The ZDC's have a resolution sigma of 7-9 cm. This is so wide that it would kill any fine res. needed esp. for PID in FS. 2) The two TPC-modules, though fundamentally different, use the same clusters and so cannot really be considered independent (?). Their main difference is that one has track-finding as a middle-layer before vtx-det - I would like some informed opinions on wether or not we should consider their outputs independent measturements! This leaves BB and one TPC-module, and I am currently (partly thorugh discussions with Yury) trying to get a handle on the sigma of the distribution of BB-vertex vs TPC-vertex as function of centrality. Also, as Ian has pointed out, the TPC-vertex is uncorrelated with the BB-vertex in up to 25% of the events - we need to remove this problem before using these two together. I have been looking through the output from BrTPMClusterVertexModule today, and I believe I can easily remove at least part of this by using one or two more internal cuts in the module Once this is dealt with it is at least my humble opinion that we should consider weighting these two results - at least if Yury's claim that the physical resolution of the BB's is 19 mm holds. Well - one cup of coffee and a bisquit's worth from me :-) ------------------------------------------------ Bjorn H. Samset Master-student in Heavy Ion physics Mob: +47 92 05 19 98 Office: +47 22 85 77 62 Adr: Kri 2A709 Sognsveien 218 0864 Oslo
This archive was generated by hypermail 2b29 : Wed Nov 08 2000 - 13:35:22 EST